advertising
Advertising is the practice and techniques employed to bring attention to a product or service. Advertising aims to put a product or service in the spotlight in hopes of drawing it attention from consumers. It is typically used to promote a ...
by an animal to potential
predators
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity,
venom
Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
, foul taste or smell, sharp spines, or aggressive nature. These advertising signals may take the form of conspicuous coloration,
sound
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...
s,
odour
An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sense ...
s, or other perceivable characteristics. Aposematic signals are beneficial for both predator and prey, since both avoid potential harm.
The term was coined in 1877 by
Edward Bagnall Poulton
Sir Edward Bagnall Poulton, FRS HFRSE FLS (27 January 1856 – 20 November 1943) was a British evolutionary biologist, a lifelong advocate of natural selection through a period in which many scientists such as Reginald Punnett doubted its ...
for
Alfred Russel Wallace
Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution through natural se ...
's concept of warning coloration. Aposematism is exploited in
Müllerian mimicry
Müllerian mimicry is a natural phenomenon in which two or more well-defended species, often foul-tasting and sharing common predators, have come to mimic each other's honest warning signals, to their mutual benefit. The benefit to Müllerian ...
, where species with strong defences evolve to resemble one another. By mimicking similarly coloured species, the warning signal to predators is shared, causing them to learn more quickly at less of a cost.
A genuine aposematic signal that a species actually possesses chemical or physical defences is not the only way to deter predators. In
Batesian mimicry
Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, after his work on bu ...
, a mimicking species resembles an aposematic model closely enough to share the protection, while many species have bluffing deimatic displays which may startle a predator long enough to enable an otherwise undefended prey to escape.
There is good evidence for aposematism in terrestrial animals; its existence in marine animals is possible but disputed.
Etymology
The term aposematism was coined by the English zoologist
Edward Bagnall Poulton
Sir Edward Bagnall Poulton, FRS HFRSE FLS (27 January 1856 – 20 November 1943) was a British evolutionary biologist, a lifelong advocate of natural selection through a period in which many scientists such as Reginald Punnett doubted its ...
in his 1890 book ''
The Colours of Animals
''The Colours of Animals'' is a zoology book written in 1890 by Sir Edward Bagnall Poulton (1856–1943). It was the first substantial textbook to argue the case for Darwinian selection applying to all aspects of animal coloration. The book a ...
''. He based the term on the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
words ἀπό ''apo'' 'away' and σῆμα ''sēma'' 'sign', referring to signs that warn other animals away.
Defence mechanism
The function of aposematism is to prevent attack, by warning potential predators that the prey animal has defences such as being unpalatable or poisonous. The easily detected warning is a primary defence mechanism, and the non-visible defences are secondary. Aposematic signals are primarily visual, using bright colours and high-contrast patterns such as stripes. Warning signals are honest indications of noxious prey, because conspicuousness evolves in tandem with noxiousness. Thus, the brighter and more conspicuous the organism, the more toxic it usually is. This is in contrast to deimatic displays, which attempt to startle a predator with a threatening appearance but which are bluffing, unsupported by any strong defences.
The most common and effective colours are red, yellow, black, and white. These colours provide strong contrast with green foliage, resist changes in shadow and lighting, are highly chromatic, and provide distance dependent
camouflage
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the ...
. Some forms of warning coloration provide this distance dependent camouflage by having an effective pattern and colour combination that do not allow for easy detection by a predator from a distance, but are warning-like from a close proximity, allowing for an advantageous balance between camouflage and aposematism. Warning coloration evolves in response to background, light conditions, and predator vision. Visible signals may be accompanied by odours, sounds or behaviour to provide a multi-modal signal which is more effectively detected by predators.
Unpalatability, broadly understood, can be created in a variety of ways. Some
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
s such as the
ladybird
Coccinellidae () is a widespread family of small beetles ranging in size from . They are commonly known as ladybugs in North America and ladybirds in Great Britain. Some entomologists prefer the names ladybird beetles or lady beetles as they ...
or
tiger moth
The de Havilland DH.82 Tiger Moth is a 1930s British biplane designed by Geoffrey de Havilland and built by the de Havilland Aircraft Company. It was operated by the Royal Air Force (RAF) and other operators as a primary trainer aircraft. ...
contain bitter-tasting chemicals, while the
skunk
Skunks are mammals in the family Mephitidae. They are known for their ability to spray a liquid with a strong, unpleasant scent from their anal glands. Different species of skunk vary in appearance from black-and-white to brown, cream or ginge ...
produces a noxious odour, and the poison glands of the
poison dart frog
Poison dart frog (also known as dart-poison frog, poison frog or formerly known as poison arrow frog) is the common name of a group of frogs in the family Dendrobatidae which are native to tropical Central and South America. These species are ...
velvet ant
The Mutillidae are a family of more than 7,000 species of wasps whose wingless females resemble large, hairy ants. Their common name velvet ant refers to their dense pile of hair, which most often is bright scarlet or orange, but may also be bl ...
or
neurotoxin
Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature ner ...
in a
black widow spider
''Latrodectus'' is a broadly distributed genus of spiders with several species that are commonly known as the true widows. This group is composed of those often loosely called black widow spiders, brown widow spiders, and similar spiders. Howeve ...
make them dangerous or painful to attack. Tiger moths advertise their unpalatability by either producing
ultrasonic
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...
noises which warn bats to avoid them, or by warning postures which expose brightly coloured body parts (see
Unkenreflex
Unkenreflex – interchangeably referred to as unken reflex (''Unke'' is the German word for the genus of fire-bellied toads) – is a defensive posture adopted by several branches of the amphibian class – including salamanders, toads, and cert ...
), or exposing eyespots. Velvet ants (actually parasitic wasps) such as '' Dasymutilla occidentalis'' both have bright colours and produce audible noises when grabbed (via
stridulation
Stridulation is the act of producing sound by rubbing together certain body parts. This behavior is mostly associated with insects, but other animals are known to do this as well, such as a number of species of fish, snakes and spiders. The mech ...
), which serve to reinforce the warning. Among mammals, predators can be dissuaded when a smaller animal is aggressive and able to defend itself, as for example in
honey badger
The honey badger (''Mellivora capensis''), also known as the ratel ( or ), is a mammal widely distributed in Africa, Southwest Asia, and the Indian subcontinent. Because of its wide range and occurrence in a variety of habitats, it is liste ...
s.
Prevalence
In terrestrial ecosystems
Aposematism is widespread in insects, but less so in
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s, being mostly confined to a smaller number of
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
,
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
, and
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
species, and some foul-smelling or aggressive
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s. Pitohuis, red and black birds whose toxic feathers and skin apparently comes from the poisonous beetles they ingest, could be included. It has been proposed that aposematism played a role in human evolution, body odour carrying a warning to predators of large
hominin
The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos) and in standard usage excludes the genus ''Gorilla'' (gorillas).
The t ...
s able to defend themselves with weapons.
Perhaps the most numerous aposematic vertebrates are the poison dart frogs (family:
Dendrobatidae
Poison dart frog (also known as dart-poison frog, poison frog or formerly known as poison arrow frog) is the common name of a group of frogs in the Family (biology), family Dendrobatidae which are native to tropical Central and South America. T ...
). These neotropical anuran amphibians exhibit a wide spectrum of coloration and toxicity. Some species in this poison frog family (particularly ''
Dendrobates
''Dendrobates'' is a genus of poison dart frogs native to Central and South America. It once contained numerous species, but most originally placed in this genus have been split off into other genera such as ''Adelphobates'', '' Ameerega'', '' A ...
'', ''
Epipedobates
''Epipedobates'' is a genus of poison dart frogs native to northern South America (Colombia and Ecuador) west of the Andes, including the western slopes. Common name phantasmal poison frogs has been suggested for the genus.
Taxonomy
''Epipedoba ...
'', and ''
Phyllobates
''Phyllobates'' is a genus of poison dart frogs native to Central and South America, from Nicaragua to Colombia. There are 3 different Colombian species of ''Phyllobates'', considered highly toxic species due to the poison they contain in the w ...
'') are conspicuously coloured and sequester one of the most toxic
alkaloid
Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar ...
s among all living species. Within the same family, there are also cryptic frogs (such as '' Colostethus'' and ''
Mannophryne
''Mannophryne'' is a genus of frogs native to Venezuela and Trinidad and Tobago
Trinidad and Tobago (, ), officially the Republic of Trinidad and Tobago, is the southernmost island country in the Caribbean. Consisting of the main islands ...
'') that lack these toxic alkaloids. Although these frogs display an extensive array of coloration and toxicity, there is very little genetic difference between the species. Evolution of their conspicuous coloration is correlated to traits such as chemical defense, dietary specialization, acoustic diversification, and increased body mass.
Some
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s are thought to employ aposematism to warn
herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
s of unpalatable chemicals or physical defences such as prickled leaves or thorns. Many insects, such as
cinnabar moth
The cinnabar moth (''Tyria jacobaeae'') is a brightly coloured arctiid moth found as a native species in Europe and western and central Asia then east across the Palearctic to Siberia to China. It has been introduced into New Zealand, Australia a ...
caterpillars, acquire toxic chemicals from their host plants. Among mammals,
skunk
Skunks are mammals in the family Mephitidae. They are known for their ability to spray a liquid with a strong, unpleasant scent from their anal glands. Different species of skunk vary in appearance from black-and-white to brown, cream or ginge ...
s and
zorilla
The striped polecat (''Ictonyx striatus''), also called the African polecat, zoril, zorille, zorilla, Cape polecat, and African skunk, is a member of the family Mustelidae that resembles a skunk (of the family Mephitidae). The name "zorilla" c ...
s advertise their foul-smelling chemical defences with sharply contrasting black-and-white patterns on their fur, while the similarly-patterned
badger
Badgers are short-legged omnivores in the family Mustelidae (which also includes the otters, wolverines, martens, minks, polecats, weasels, and ferrets). Badgers are a polyphyletic rather than a natural taxonomic grouping, being united by ...
and
honey badger
The honey badger (''Mellivora capensis''), also known as the ratel ( or ), is a mammal widely distributed in Africa, Southwest Asia, and the Indian subcontinent. Because of its wide range and occurrence in a variety of habitats, it is liste ...
advertise their sharp claws, powerful jaws, and aggressive natures. Some brightly coloured birds such as
passerine
A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by t ...
s with contrasting patterns may also be aposematic, at least in females; but since male birds are often brightly coloured through
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
, and their coloration is not correlated with edibility, it is unclear whether aposematism is significant.
The sound-producing rattle of
rattlesnake
Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small anim ...
s is an acoustic form of aposematism. Sound production by the caterpillar of the Polyphemus moth, ''
Antheraea polyphemus
''Antheraea polyphemus'', the Polyphemus moth, is a North American member of the family Saturniidae, the giant silk moths. It is a tan-colored moth, with an average wingspan of 15 cm (6 in). The most notable feature of the moth is its ...
'', may similarly be acoustic aposematism, connected to and preceded by chemical defences. Similar acoustic defences exist in a range of
Bombycoidea
Bombycoidea is a superfamily of moths. It contains the silk moths, emperor moths, sphinx moths
The Sphingidae are a family of moths ( Lepidoptera) called sphinx moths, also colloquially known as hawk moths, with many of their caterpillars ...
caterpillars.
In marine ecosystems
The existence of aposematism in marine ecosystems is controversial. Many marine organisms, particularly those on coral reefs, are brightly coloured or patterned, including sponges, corals, molluscs and fish, with little or no connection to chemical or physical defenses. Caribbean reef
sponge
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...
s are brightly coloured, and many species are full of toxic chemicals, but there is no statistical relationship between the two factors.
Nudibranch
Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to matc ...
molluscs are the most commonly cited examples of aposematism in marine ecosystems, but the evidence for this has been contested, mostly because (1) there are few examples of mimicry among species, (2) many species are nocturnal or cryptic, and (3) bright colours at the red end of the colour spectrum are rapidly attenuated as a function of water depth. For example, the Spanish Dancer nudibranch (genus '' Hexabranchus''), among the largest of tropical marine slugs, potently chemically defended, and brilliantly red and white, is nocturnal and has no known mimics. Mimicry is to be expected as
Batesian mimic
Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, after his work on bu ...
s with weak defences can gain a measure of protection from their resemblance to aposematic species. Other studies have concluded that nudibranchs such as the slugs of the family
Phyllidiidae
Phyllidiidae is a family of sea slugs, dorid nudibranchs, marine gastropod mollusks in the superfamily Phyllidioidea.
This family is within the clade Doridacea (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005).
Distributi ...
from Indo-Pacific coral reefs are aposematically coloured.
Müllerian mimicry
Müllerian mimicry is a natural phenomenon in which two or more well-defended species, often foul-tasting and sharing common predators, have come to mimic each other's honest warning signals, to their mutual benefit. The benefit to Müllerian ...
has been implicated in the coloration of some Mediterranean nudibranchs, all of which derive defensive chemicals from their sponge diet.
The
crown-of-thorns starfish
The crown-of-thorns starfish (frequently abbreviated to COTS), ''Acanthaster planci'', is a large starfish that preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns starfish receives its name from venomous thorn-like spine ...
, like other starfish such as '' Metrodira subulata'', has conspicuous coloration and conspicuous long, sharp spines, as well as cytolytic
saponin
Saponins (Latin "sapon", soap + "-in", one of), also selectively referred to as triterpene glycosides, are bitter-tasting usually toxic plant-derived organic chemicals that have a foamy quality when agitated in water. They are widely distributed ...
s, chemicals which could function as an effective defence; this evidence is argued to be sufficient for such species to be considered aposematic.
It has been proposed that aposematism and mimicry is less evident in marine invertebrates than terrestrial insects because predation is a more intense selective force for many insects, which disperse as adults rather than as larvae and have much shorter generation times. Further, there is evidence that fish predators such as
bluehead
''Thalassoma amblycephalum'', the blunt-headed wrasse, blue-headed wrasse, blue-headed zoe, moon wrasse, paddle-fin wrasse or two-tone wrasse, is a species of wrasse native to the Indian Ocean and the western Pacific Ocean. It is a reef inhabita ...
s may adapt to visual cues more rapidly than do birds, making aposematism less effective.
Blue-ringed octopus
Blue-ringed octopuses, comprising the genus ''Hapalochlaena'', are four highly venomous species of octopus that are found in tide pools and coral reefs in the Pacific and Indian oceans, from Japan to Australia. They can be identified by their ye ...
es are venomous. They spend much of their time hiding in crevices whilst displaying effective camouflage patterns with their dermal
chromatophore
Chromatophores are cells that produce color, of which many types are Biological pigment, pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and ...
cells. However, if they are provoked, they quickly change colour, becoming bright yellow with each of the 50-60 rings flashing bright iridescent blue within a third of a second. It is often stated this is an aposematic warning display, but the hypothesis has rarely if ever been tested.
Behaviour
The mechanism of defence relies on the
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
of the would-be predator; a bird that has once experienced a foul-tasting
grasshopper
Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is possibly the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago.
Grasshopp ...
will endeavour to avoid a repetition of the experience. As a consequence, aposematic species are often gregarious. Before the memory of a bad experience attenuates, the predator may have the experience reinforced through repetition. Aposematic organisms often move in a languid fashion, as they have little need for speed and agility. Instead, their morphology is frequently tough and resistant to injury, thereby allowing them to escape once the predator is warned off.
Aposematic species do not need to hide or stay still as cryptic organisms do, so aposematic individuals benefit from more freedom in exposed areas and can spend more time foraging, allowing them to find more and better quality food. They may also be able to make use of conspicuous mating displays, including vocal signals, which may then develop through
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
.
Origins of the theory
Wallace, 1867
In a letter to
Alfred Russel Wallace
Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution through natural se ...
dated 23 February 1867,
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
wrote, "On Monday evening I called on
Bates
Bates may refer to:
Places
* Bates, Arkansas, an unincorporated community
* Bates, Illinois. an unincorporated community in Sangamon County
* Bates, Michigan, a community in Grand Traverse County
* Bates, New York, a hamlet in the town of Ell ...
& put a difficulty before him, which he could not answer, & as on some former similar occasion, his first suggestion was, 'you had better ask Wallace'. My difficulty is, why are caterpillars sometimes so beautifully & artistically coloured?" Darwin was puzzled because his theory of
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
(where females choose their mates based on how attractive they are) could not apply to caterpillars since they are immature and hence not sexually active.
Wallace replied the next day with the suggestion that since some caterpillars "...are protected by a disagreeable taste or odour, it would be a positive advantage to them never to be mistaken for any of the palatable catterpillars 'sic'' because a slight wound such as would be caused by a peck of a bird’s bill almost always I believe kills a growing . Any gaudy & conspicuous colour therefore, that would plainly distinguish them from the brown & green eatable , would enable birds to recognise them easily as at a kind not fit for food, & thus they would escape seizure which is as bad as being eaten."
Since Darwin was enthusiastic about the idea, Wallace asked the
Entomological Society of London
The Royal Entomological Society is devoted to the study of insects. Its aims are to disseminate information about insects and improving communication between entomologists.
The society was founded in 1833 as the Entomological Society of Londo ...
to test the hypothesis. In response, the entomologist John Jenner Weir conducted experiments with caterpillars and birds in his aviary, and in 1869 he provided the first experimental evidence for warning coloration in animals. The evolution of aposematism surprised 19th-century naturalists because the probability of its establishment in a population was presumed to be low, since a conspicuous signal suggested a higher chance of predation.
Poulton, 1890
Wallace coined the term "warning colours" in an article about animal coloration in 1877. In 1890
Edward Bagnall Poulton
Sir Edward Bagnall Poulton, FRS HFRSE FLS (27 January 1856 – 20 November 1943) was a British evolutionary biologist, a lifelong advocate of natural selection through a period in which many scientists such as Reginald Punnett doubted its ...
renamed the concept ''aposematism'' in his book ''
The Colours of Animals
''The Colours of Animals'' is a zoology book written in 1890 by Sir Edward Bagnall Poulton (1856–1943). It was the first substantial textbook to argue the case for Darwinian selection applying to all aspects of animal coloration. The book a ...
''. He described the derivation of the term as follows:
Evolution
Aposematism is paradoxical in
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary terms, as it makes individuals conspicuous to predators, so they may be killed and the trait eliminated before predators learn to avoid it. If warning coloration puts the first few individuals at such a strong disadvantage, it would never last in the species long enough to become beneficial.
Supported explanations
There is evidence for explanations involving dietary conservatism, in which predators avoid new prey because it is an unknown quantity; this is a long-lasting effect. Dietary conservatism has been demonstrated experimentally in some species of birds and fish.
Further, birds recall and avoid objects that are both conspicuous and foul-tasting longer than objects that are equally foul-tasting but cryptically coloured. This suggests that Wallace's original view, that warning coloration helped to teach predators to avoid prey thus coloured, was correct. However, some birds (inexperienced starlings and domestic chicks) also